This invention relates to a process for the production of compression-molded materials, preferably chipboards, by the compression molding of ligno-cellulose-containing starting materials mixed and/or impregnated with polyisocyanates as binder using new, latent, heat-activatable catalysts based on ammonium salts (which term includes tetraalkylammonium salts) of the type obtainable by reacting primary, secondary and/or tertiary amines with alkyl esters of acids of phosphorus exerting alkylating properties against the amines.
Compression-molded materials, such as for example chipboards, laminates or other moldings, are usually produced by compression-molding the inorganic or organic starting material (for example a mass of wood chips, wood fibers and/or other lignocellulose-containing material) with polyisocyanates, water and optionally polyols; or other binders, such as urea/formaldehyde or phenol/formaldehyde resins. The use of polyisocyanates as binder improves the stability and moisture behavior of the products and their mechanical properties. In addition, polyisocyanates as binders have significant advantages in terms of process technology, as disclosed for example in German Offenlegungsschrift No. 2,109,686.
In principle, catalysts of the type known from polyurethane chemistry (for example those mentioned on pages 26 to 29 and 31 to 33 of German Offenlegungsschrift No. 2,854,384) may also be used in conventional processes (cf. for example German Auslegeschrift No. 2,711,958) to shorten molding times. This is particularly important in the case of so-called single-platen presses. In that case, however, undesirable foaming and premature setting generally occur during the actual mixing of the components and during storage of the isocyanate-coated chips pending compression molding due to the catalytic effect which is immediately exerted upon the reactive NCO-groups. Accordingly, the compression molding process must be carried out in the absence of catalysts, i.e. over prolonged periods.